During the past quarter century, the automotive industry has made great strides in reducing vibration, especially vibration which creates annoying noise levels. However, there is a need for a substantial reduction in the vibration of components which have high operating temperatures, especially vibration emanating from diesel engines. It has long been known that such vibrations could be substantially reduced by damping external surfaces of engine components and attachments such as the valve cover, the valley cover, mounting brackets and the oil pan, and that such vibrations could be substantially damped by forming such surfaces from a composite of a viscoelastic layer constrained by a pair of metal sheets. However, the automotive industry has not known a viscoelastic material which could effectively damp vibrations at the elevated operating temperatures while retaining such capability after prolonged exposure to the heat of the engine.
Typical of prior art concerning constrained-layer damping for automotive engines is "Diesel-Engine Noise Can Be Reduced", Automotive Engineering, Jan. 1973, pages 42-45, which suggests a deep oil pan made from double-skinned, damped sheet metal. As for free-layer damping, "Lowering Diesel Noise Through Hardware Modifications", Automotive Engineering, June 1973, pages 41-47, suggests butyl rubber 1/4 inch thick bonded to the top of a standard valve cover. We have not found any publication dealing with constrained-layer damping of vibrations in automotive engines or other machines having high operating temperatures that identifies specific viscoelastic materials.
The same problem is involved in the need for damping vibrations at the surfaces of other machines or devices having high operating temperatures such as steam lines and high-voltage electrical transformers.